Numerical Study of Steady-Blowing Jet for a Stalled Airfoil

Abstract

Numerical study on flow separation control is conducted for a stalled airfoil with steady-blowing jet. It is expected that steady-blowing jet, if it is applied properly, provides additional momentum in the boundary layer flow which is susceptible to flow separation at high angles of attack. Various methods have been tested to control the stall with fluidic actuation. Major parameters in fluidic actuation are the jet location, the jet momentum, the jet angle and so on. In this study, of interest is the impact of the jet angle ($\theta_j$) on the flow control. The jet angles is the angle between the jet direction and the airfoil surface. The current study is conducted with two jet angles: 22 degrees (tangential jet) and 80 degrees (chord-normal jet). A rotorcraft-relevant flow condition is simulated with a compressible Navier-Stokes solver. The governing equations of unsteady Reynolds-averaged Navier-Stokes are numerically solved. Both static and pitching conditions of a rotor airfoil are simulated to investigate the flow control in various situations. Current 2D simulations indicate that the small jet angle 22 degrees is effective to control the stall. This tangential jet can provide additional momentum into the separating boundary layer directly. In contrast, the chord-normal jet of 80 degrees cuts through the boundary layer and blocks the external flow, resulting in a significant degrade in the aerodynamic lift. Current 3D simulation indicates that a chord-normal jet from a discrete hole in the span can induce secondary vortex which helps to mitigate the boundary layer separation on the airfoil.